Recently, a technique has been proposed for assisting a vehicle driver in accordance with his or her driving act with using a face tracking device mounted to a vehicle. The face tracking device tracks an orientation of a person's face based on image data of the person's face. In the above-described technique, the orientation of a vehicle driver's face is used as an informational item to assist the vehicle driver. An orientation of a person's face is referred to herein as a facial orientation.
An appearance model and a cylindrical head model are known methods for detecting the facial orientation based on an image data. A reference of the appearance model is, for example, given by I. Matthews and S. Baker, International Journal of Computer Vision, 2004, Vol. 60, No. 2, pp. 135-164. A reference of the cylindrical head model is, for example, given by J. Xaio et al., International Journal of Imaging Systems and Technology, 2003, Vol. 13, No. 2, pp. 85-94.
According to the appearance model, the facial orientation of a person is capable of being tracked when the facial orientation is between +10-degree and −10-degree around the vertical axis. The 0-degree angle of the facial orientation around the vertical axis corresponds to a case where the person faces front. When the vehicle driver is confirming safe conditions by looking right and left, an angle of the facial orientation may be changeable up to 60-degree or the like. Therefore, it is difficult to detect safety confirmation behavior done by the vehicle driver with using the appearance model.
According to the cylindrical head model, an orientation of a person's face is capable of being tracked even when the orientation angle is large.
However, a problem associated with the above-described cylindrical head model is that, unless frontal facial image data is manually set in advance, the cylindrical head model is not utilized.